H₂S removal

Sulfur species such as H2S need to be removed to very low concentrations for safety, corrosion, and environmental impact reasons, and for downstream catalytic processes. Sulfur removal targets are often driven by global standardization, such as maximum allowable concentration in natural gas transported over pipeline or in liquid form.

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Complete sulfur removal

Typical pipeline specifications are between 4 and 16 ppmv. Specifications may also be expressed in grains of sulfur per 100 SCF; 0.5 grains/100SCF is equivalent to 4 ppmv. Also in other applications, such as refinery gases and syngas treatment, there is a general desire to reduce H2S to very low levels, although the exact specification can be plant specific.

Selective sulfur removal

In addition to the objective of complete sulfur removal there is an additional objective to minimize CO2 absorption. Where an acid gas stream is to be processed in a sulfur recovery unit based on Claus technology, the acid gas must contain a minimum concentration of H2S of e.g. 40 volume percent. In the case of natural gas treatment, where gas is sent to pipeline, CO2 may not need to be removed; it can actually be cost-inefficient since it leads to a larger acid gas removal system and reduces the amount of gas that can be sold. In applications such as tail gas treatment and acid gas enrichment, there is an additional challenge of very low feed gas pressure. While tertiary amines, such as MDEA, are generally preferred for selective sulfur removal because of the slow kinetics with CO2 they are also “weaker” amines, lowering the driving force for absorption at lower pressure. Eastman AdapT solvents accommodate through improved mass transfer and solvent regenerability, improving the chemical equilibrium for absorption of H2S.